/// ----------------------------------------------------------------------------------------
/// <summary>
/// Decrypt and deserialize SEB settings
/// When forEditing = true, then the decrypting password the user entered and/or
/// certificate reference found in the .seb file is returned
/// </summary>
/// ----------------------------------------------------------------------------------------
public static DictObj DecryptSEBSettings(byte[] sebData, bool forEditing, ref string sebFilePassword, ref bool passwordIsHash, ref X509Certificate2 sebFileCertificateRef, bool suppressFileFormatError = false)
{
// Ungzip the .seb (according to specification >= v14) source data
byte[] unzippedSebData = GZipByte.Decompress(sebData);
// if unzipped data is not null, then unzipping worked, we use unzipped data
// if unzipped data is null, then the source data may be an uncompressed .seb file, we proceed with it
if (unzippedSebData != null)
{
sebData = unzippedSebData;
}
string prefixString;
// save the data including the first 4 bytes for the case that it's acutally an unencrypted XML plist
byte[] sebDataUnencrypted = sebData.Clone() as byte[];
// Get 4-char prefix
prefixString = GetPrefixStringFromData(ref sebData);
//// Check prefix identifying encryption modes
/// Check for new Multipart and Custom headers
// Multipart Config File: The first part containts the regular SEB key/value settings
// following parts can contain additional resources. An updated SEB version will be
// able to read and process those parts sequentially as a stream.
// Therefore potentially large additional resources won't have to be loaded into memory at once
if (prefixString.CompareTo(MULTIPART_MODE) == 0)
{
// Skip the Multipart Config File header
byte[] multipartConfigLengthData = GetPrefixDataFromData(ref sebData, MULTIPART_LENGTH);
long multipartConfigLength = BitConverter.ToInt64(multipartConfigLengthData, 0);
Logger.AddInformation("Multipart Config File, first part (settings) length: " + multipartConfigLength);
try
{
Logger.AddInformation("Cropping config file, as this SEB version cannot process additional parts of multipart config files.");
byte[] dataFirstPart = new byte[sebData.Length - multipartConfigLength];
Buffer.BlockCopy(sebData, 0, dataFirstPart, 0, dataFirstPart.Length);
sebData = dataFirstPart;
}
catch (Exception ex)
{
Logger.AddError("Error while cropping config file", null, ex, ex.Message);
}
}
// Custom Header: Containts a 32 bit value for the length of the header
// followed by the custom header information. After the header, regular
// SEB config file data follows
if (prefixString.CompareTo(CUSTOM_HEADER_MODE) == 0)
{
// Skip the Custom Header
byte[] customHeaderLengthData = GetPrefixDataFromData(ref sebData, CUSTOMHEADER_LENGTH);
int customHeaderLength = BitConverter.ToInt32(customHeaderLengthData, 0);
Logger.AddInformation("Custom Config File Header length: " + customHeaderLength);
try
{
Logger.AddInformation("Removing custom header from config file data. This SEB version cannot process this header type and will ignore it.");
byte[] customHeaderData = GetPrefixDataFromData(ref sebData, customHeaderLength);
Logger.AddInformation("Custom header data: " + customHeaderData);
}
catch (Exception ex)
{
Logger.AddError("Error while removing custom header from config file data", null, ex, ex.Message);
}
}
// Prefix = pksh ("Public-Symmetric Key Hash") ?
if (prefixString.CompareTo(PUBLIC_SYMMETRIC_KEY_MODE) == 0)
{
// Decrypt with cryptographic identity/private and symmetric key
sebData = DecryptDataWithPublicKeyHashPrefix(sebData, true, forEditing, ref sebFileCertificateRef);
if (sebData == null)
{
return(null);
}
// Get 4-char prefix again
// and remaining data without prefix, which is either plain or still encoded with password
prefixString = GetPrefixStringFromData(ref sebData);
}
// Prefix = pkhs ("Public Key Hash") ?
if (prefixString.CompareTo(PUBLIC_KEY_HASH_MODE) == 0)
{
// Decrypt with cryptographic identity/private key
sebData = DecryptDataWithPublicKeyHashPrefix(sebData, false, forEditing, ref sebFileCertificateRef);
if (sebData == null)
{
return(null);
}
// Get 4-char prefix again
// and remaining data without prefix, which is either plain or still encoded with password
prefixString = GetPrefixStringFromData(ref sebData);
}
// Prefix = pswd ("Password") ?
if (prefixString.CompareTo(PASSWORD_MODE) == 0)
{
// Decrypt with password
// if the user enters the right one
byte[] sebDataDecrypted = null;
string password;
// Allow up to 5 attempts for entering decoding password
string enterPasswordString = SEBUIStrings.enterPassword;
int i = 5;
do
{
i--;
// Prompt for password
password = SebPasswordDialogForm.ShowPasswordDialogForm(SEBUIStrings.loadingSettings, enterPasswordString);
if (password == null)
{
return(null);
}
//error = nil;
sebDataDecrypted = SEBProtectionController.DecryptDataWithPassword(sebData, password);
enterPasswordString = SEBUIStrings.enterPasswordAgain;
// in case we get an error we allow the user to try it again
} while ((sebDataDecrypted == null) && i > 0);
if (sebDataDecrypted == null)
{
//wrong password entered in 5th try: stop reading .seb file
MessageBox.Show(SEBUIStrings.decryptingSettingsFailed, SEBUIStrings.decryptingSettingsFailedReason, MessageBoxButtons.OK, MessageBoxIcon.Error);
return(null);
}
sebData = sebDataDecrypted;
// If these settings are being decrypted for editing, we return the decryption password
if (forEditing)
{
sebFilePassword = password;
}
}
else
{
// Prefix = pwcc ("Password Configuring Client") ?
if (prefixString.CompareTo(PASSWORD_CONFIGURING_CLIENT_MODE) == 0)
{
// Decrypt with password and configure local client settings
// and quit afterwards, returning if reading the .seb file was successfull
DictObj sebSettings = DecryptDataWithPasswordForConfiguringClient(sebData, forEditing, ref sebFilePassword, ref passwordIsHash);
return(sebSettings);
}
else
{
// Prefix = plnd ("Plain Data") ?
if (prefixString.CompareTo(PLAIN_DATA_MODE) != 0)
{
// No valid 4-char prefix was found in the .seb file
// Check if .seb file is unencrypted
if (prefixString.CompareTo(UNENCRYPTED_MODE) == 0)
{
// .seb file seems to be an unencrypted XML plist
// get the original data including the first 4 bytes
sebData = sebDataUnencrypted;
}
else
{
// No valid prefix and no unencrypted file with valid header
// cancel reading .seb file
if (!suppressFileFormatError)
{
MessageBox.Show(SEBUIStrings.settingsNotUsable, SEBUIStrings.settingsNotUsableReason, MessageBoxButtons.OK, MessageBoxIcon.Error);
}
return(null);
}
}
}
}
// If we don't deal with an unencrypted seb file
// ungzip the .seb (according to specification >= v14) decrypted serialized XML plist data
if (prefixString.CompareTo(UNENCRYPTED_MODE) != 0)
{
sebData = GZipByte.Decompress(sebData);
}
// Get preferences dictionary from decrypted data
DictObj sebPreferencesDict = GetPreferencesDictFromConfigData(sebData, forEditing);
// If we didn't get a preferences dict back, we abort reading settings
if (sebPreferencesDict == null)
{
return(null);
}
// We need to set the right value for the key sebConfigPurpose to know later where to store the new settings
sebPreferencesDict[SEBSettings.KeySebConfigPurpose] = (int)SEBSettings.sebConfigPurposes.sebConfigPurposeStartingExam;
// Reading preferences was successful!
return(sebPreferencesDict);
}
/// ----------------------------------------------------------------------------------------
/// <summary>
/// Helper method which decrypts the byte array using an empty password,
/// or the administrator password currently set in SEB
/// or asks for the password used for encrypting this SEB file
/// for configuring the client
/// </summary>
/// ----------------------------------------------------------------------------------------
private static DictObj DecryptDataWithPasswordForConfiguringClient(byte[] sebData, bool forEditing, ref string sebFilePassword, ref bool passwordIsHash)
{
passwordIsHash = false;
string password;
// First try to decrypt with the current admin password
// get admin password hash
string hashedAdminPassword = (string)SEBSettings.valueForDictionaryKey(SEBSettings.settingsCurrent, SEBSettings.KeyHashedAdminPassword);
if (hashedAdminPassword == null)
{
hashedAdminPassword = "";
}
// We use always uppercase letters in the base16 hashed admin password used for encrypting
hashedAdminPassword = hashedAdminPassword.ToUpper();
DictObj sebPreferencesDict = null;
byte[] decryptedSebData = SEBProtectionController.DecryptDataWithPassword(sebData, hashedAdminPassword);
if (decryptedSebData == null)
{
// If decryption with admin password didn't work, try it with an empty password
decryptedSebData = SEBProtectionController.DecryptDataWithPassword(sebData, "");
if (decryptedSebData == null)
{
// If decryption with empty and admin password didn't work, ask for the password the .seb file was encrypted with
// Allow up to 5 attempts for entering decoding password
int i = 5;
password = null;
string enterPasswordString = SEBUIStrings.enterEncryptionPassword;
do
{
i--;
// Prompt for password
password = SebPasswordDialogForm.ShowPasswordDialogForm(SEBUIStrings.reconfiguringLocalSettings, enterPasswordString);
// If cancel was pressed, abort
if (password == null)
{
return(null);
}
string hashedPassword = SEBProtectionController.ComputePasswordHash(password);
// we try to decrypt with the hashed password
decryptedSebData = SEBProtectionController.DecryptDataWithPassword(sebData, hashedPassword);
// in case we get an error we allow the user to try it again
enterPasswordString = SEBUIStrings.enterEncryptionPasswordAgain;
} while (decryptedSebData == null && i > 0);
if (decryptedSebData == null)
{
//wrong password entered in 5th try: stop reading .seb file
MessageBox.Show(SEBUIStrings.reconfiguringLocalSettingsFailed, SEBUIStrings.reconfiguringLocalSettingsFailedWrongPassword, MessageBoxButtons.OK, MessageBoxIcon.Error);
return(null);
}
else
{
// Decrypting with entered password worked: We save it for returning it later
if (forEditing)
{
sebFilePassword = password;
}
}
}
}
else
{
//decrypting with hashedAdminPassword worked: we save it for returning as decryption password
sebFilePassword = hashedAdminPassword;
// identify that password as hash
passwordIsHash = true;
}
/// Decryption worked
// Ungzip the .seb (according to specification >= v14) decrypted serialized XML plist data
decryptedSebData = GZipByte.Decompress(decryptedSebData);
// Check if the openend reconfiguring seb file has the same admin password inside like the current one
try
{
sebPreferencesDict = (DictObj)Plist.readPlist(decryptedSebData);
}
catch (Exception readPlistException)
{
// Error when deserializing the decrypted configuration data
// We abort reading the new settings here
MessageBox.Show(SEBUIStrings.loadingSettingsFailed, SEBUIStrings.loadingSettingsFailedReason, MessageBoxButtons.OK, MessageBoxIcon.Error);
Console.WriteLine(readPlistException.Message);
return(null);
}
// Get the admin password set in these settings
string sebFileHashedAdminPassword = (string)SEBSettings.valueForDictionaryKey(sebPreferencesDict, SEBSettings.KeyHashedAdminPassword);
if (sebFileHashedAdminPassword == null)
{
sebFileHashedAdminPassword = "";
}
// Has the SEB config file the same admin password inside as the current settings have?
if (String.Compare(hashedAdminPassword, sebFileHashedAdminPassword, StringComparison.OrdinalIgnoreCase) != 0)
{
//No: The admin password inside the .seb file wasn't the same as the current one
if (forEditing)
{
// If the file is openend for editing (and not to reconfigure SEB)
// we have to ask the user for the admin password inside the file
if (!askForPasswordAndCompareToHashedPassword(sebFileHashedAdminPassword, forEditing))
{
// If the user didn't enter the right password we abort
return(null);
}
}
else
{
// The file was actually opened for reconfiguring the SEB client:
// we have to ask for the current admin password and
// allow reconfiguring only if the user enters the right one
// We don't check this for the case the current admin password was used to encrypt the new settings
// In this case there can be a new admin pw defined in the new settings and users don't need to enter the old one
if (passwordIsHash == false && hashedAdminPassword.Length > 0)
{
// Allow up to 5 attempts for entering current admin password
int i = 5;
password = null;
string hashedPassword;
string enterPasswordString = SEBUIStrings.enterCurrentAdminPwdForReconfiguring;
bool passwordsMatch;
do
{
i--;
// Prompt for password
password = SebPasswordDialogForm.ShowPasswordDialogForm(SEBUIStrings.reconfiguringLocalSettings, enterPasswordString);
// If cancel was pressed, abort
if (password == null)
{
return(null);
}
if (password.Length == 0)
{
hashedPassword = "";
}
else
{
hashedPassword = SEBProtectionController.ComputePasswordHash(password);
}
passwordsMatch = (String.Compare(hashedPassword, hashedAdminPassword, StringComparison.OrdinalIgnoreCase) == 0);
// in case we get an error we allow the user to try it again
enterPasswordString = SEBUIStrings.enterCurrentAdminPwdForReconfiguringAgain;
} while (!passwordsMatch && i > 0);
if (!passwordsMatch)
{
//wrong password entered in 5th try: stop reading .seb file
MessageBox.Show(SEBUIStrings.reconfiguringLocalSettingsFailed, SEBUIStrings.reconfiguringLocalSettingsFailedWrongCurrentAdminPwd, MessageBoxButtons.OK, MessageBoxIcon.Error);
return(null);
}
}
}
}
// We need to set the right value for the key sebConfigPurpose to know later where to store the new settings
sebPreferencesDict[SEBSettings.KeySebConfigPurpose] = (int)SEBSettings.sebConfigPurposes.sebConfigPurposeConfiguringClient;
// Reading preferences was successful!
return(sebPreferencesDict);
}